Having tierings as stratified as they are whilst max level stays at 65 (and therefore, the xp from zone x will always be just as good per mob as it ever was for you) is what leads to these zones becoming easy, low-risk xp farms. Content almost never becomes truly trivialized. You can't simply increase the xp rate in more difficult zones, AE tanking will always be viable in some form once you've acquired enough gear (XP would explode exponentially). We have 9 tiers of raid content, and the difference between each in terms of gear is pretty damn substantial. Some more than others, of course (5-6 is huge, as is 7-8 and 8-9), but the difference between a tier 4 toon and a tier 8 toon is like night and day. How do you balance group content when both of these exist and get the same xp off of the same mob? You can create zones that the tier 4 toon cannot effectively access, but you can't really keep the tier 8 player out of the content designed for the tier 4 toon, and that is what causes most of our class balance issues here.
I will say I'm pretty happy where my class is right now - being a well-geared player. Low-end warriors are terrible. If I were to make any changes to tanks, I would leave warriors and paladins alone, and give the SK a boost to hate and lifetap healing in some form that has scalability. I'd consider some form of addition to utility as well, but SK utility already exists in the form of FD and is poorly utilized by most people who actually play the class (in my experience). The limited utility an SK has in the form of buffs is made generally useless.
Heres a random idea off the top of my head, its minor, and I came up with it in 5 minutes at 6am, but its an interesting solution (to a non-problem?):
I have trouble in raids with getting SKs to hate buff me, they bitch about recast, or wanting to use it on themselves, or are just plain lazy, and it eats a buff slot, blah blah. So add a unique aug slot to weapons (we have ones that aren't being used), give SKs a spell to summon an item that creates an aug (a la searfires) to fit that slot that could provide a universal +aggr effect that stacks with +aggression
Or maybe something else fun like:
Hate procs
Lifetap procs
Mana taps
Small necro-type DoTs
Poison DDs
Holy shit batman, lore-centric, stacking utility for shadowknights! Who would have thought this was possible? Maybe a recourse like shared mind? Who the fuck knows.